Researchers have worked out the optimal recipe for making giant, long-lasting soap bubbles. It should allow anyone to reliably blow bubbles at least 12 centimetres across and potentially create some large enough to envelop a person.
Marina Pasquet, who carried out the work with her colleagues at the University of Paris-Saclay, started the project by investigating liquids that artists and performers were using to make giant bubbles. “There are a lot of recipes out there,” says Pasquet, who is now at the University of California, Berkeley.
Soap bubbles are essentially packages of air surrounded by an iridescent liquid film. A phenomenon known as the Marangoni effect, which influences the flow of molecules on the surface of bubbles, helps to keep their surface intact.
The amount of detergent has to strike a balance: with more detergent, the bubbles become easier to blow, but their lifespan also drops, says Pasquet.
That is probably all that most people would add at home, but the researchers found that two extra ingredients can lift your bubbles to another level. Chemicals called long aqueous polymers increase a characteristic known as elongational viscosity, keeping the film of the bubble stable as you blow it, says Pasquet. Common examples include J-Lube, which is an obstetrical lubricant used by vets, and the food additives guar gum and xanthan gum.
The final key ingredient is a little glycerol, also known as glycerine, which helps the ingredients mix well so the solution consistently forms bubbles. The glycerol can also slow evaporation of the water in the bubble’s film, which allows it to last for longer, says the team.
The ideal recipe, according to the researchers, is 85.9 percent water, 4 percent washing-up liquid, 0.1 percent guar gum, and 10 percent glycerol. This mix enabled the team to reliably create big, long-lasting bubbles. One example, about 12 centimetres across, lasted 24 hours in the lab, says Pasquet.
